Known dry-cleaning processes consist of a wash, rinse, and drying cycle with solvent recovery. Garments are loaded into a basket in a cleaning drum and immersed in a dry-cleaning fluid or solvent, which is pumped into the cleaning drum from a base tank. Conventional dry-cleaning fluids include perchloroethylene (PCE), petroleum-based or Stoddard solvents, CFC-113, and 1,1,1-trichloroethane, all of which are generally aided by a detergent. The solvent is used to dissolve soluble contaminants, such as oils, and to entrain and wash away insoluble contaminants, such as dirt.
The use of these conventional solvents, however, poses a number of health and safety risks as well as being environmentally hazardous. For example, halogenated solvents are known to be environmentally unfriendly, and at least one of these solvents, PCE, is a suspected carcinogen. Known petroleum-based solvents are flammable and can contribute to the production of smog. Accordingly, dry cleaning systems which utilize dense phase fluids, such as liquid carbon dioxide, as a cleaning medium have been developed. An apparatus and method for employing liquid carbon dioxide as the dry-cleaning solvent is disclosed in U.S. Pat. No. 5,467,492, entitled "Dry-Cleaning Garments Using Liquid Carbon Dioxide Under Agitation As Cleaning Medium". A similar dry cleaning apparatus is also disclosed in U.S. Pat. No. 5,651,276.
These systems pose a number of other problems, particularly in relation to the high operating pressures necessary for maintaining the gas in a liquid state. For example, the various pressurized components of the system must be constructed with thick, heavy walled structures to withstand the elevated pressures encountered during the dry cleaning operation. This, however, increases both the material cost of these components and the structures necessary to support these components.
The dry-cleaning industry is a highly competitive market which primarily consists of small neighborhood operations. Accordingly, maintaining the costs of a liquid carbon dioxide dry cleaning system as low as possible is extremely important. In addition, due to the "neighborhood" nature of many dry cleaning operations there are significant space limitations on the equipment. Thus, while maintaining the cost and space requirements to a minimum is always an important object, it is particularly critical with dry cleaning equipment.
One of the most critical components in a liquid carbon dioxide dry cleaning system both in terms of cost and space restrictions are the tanks and vessels within which the carbon dioxide is stored. Since these tanks must keep the carbon dioxide at a high pressure (e.g. 500-850 psi) under ambient temperature conditions, heavy walled pressure vessels are required. In addition, since the pressure vessels must be capable of storing a substantial quantity of liquid carbon dioxide, relatively large pressure vessels must be used. As the cost of conventional cylindrical pressure vessels generally increases linearly with their capacity, the cost of the pressure vessels alone in a liquid carbon dioxide dry cleaning system may make conversion to such a system prohibitively expensive for many dry cleaner operators. In addition, conventional pressure vessels which meet these requirements are quite bulky and heavy. Accordingly, a significant amount of space within the dry cleaning apparatus must be committed exclusively to the pressure vessels. Moreover, relatively expensive support framing, which takes up even more space, also must be provided.